Computer Programming with C++

Overview

We understand from Chapters 1 and 2 that instructions in a program are executed in a sequence in which we write them in the main() function. Such an execution is called a sequential execution. In many cases it is required to change the sequence of executing instructions based on some condition. The statements that can be used to alter the sequence of executing instructions at run time of the program are called branching or decision making control statements.

C/C++ supports a following branching/decision making control statements:

In this chapter we discuss the syntax and working of each of the above decision making control statements supported by C/C++.

if else Statement

The if-else statement is used to change the sequence of execution by evaluating a specified condition at run time of the program. The condition to be evaluated must be specified in round parenthesis when defining the if block as shown in Figure 4.1. The if-else statement defines two blocks, the first block is called if block and the second block is called else block. The control of execution is transferred inside the if block if the condition specified in the parentheses is evaluated as true, whereas the control of execution is transferred inside the else block if the condition specified is evaluated as false.

A condition is generally written using relational operators and hence an evaluation of a condition can result into two possible outcomes as ‘true’ or ‘false’. Therefore, it will be correct to say that, in any of the given scenario the control of execution will always be transferred to at least one of the two blocks (if block or the else block). Also, the control of execution will be transferred to exactly one of the two blocks (if block in case the condition is evaluated as true or it can be a else block in case the condition is evaluated as ‘false’).